Groups > comp.databases.postgresql > #263

Re: Constraints for R/O ./data/{base, et al.}

From	"Laurenz Albe" <invite@spam.to.invalid>
Newsgroups	comp.databases.postgresql
References	(1 earlier) <1317281868.445091@proxy.dienste.wien.at> <j6m21t$3bt$1@speranza.aioe.org> <1317975042.921423@proxy.dienste.wien.at> <j6nfdi$mfh$1@speranza.aioe.org> <1318258124.527489@proxy.dienste.wien.at>
Subject	Re: Constraints for R/O ./data/{base, et al.}
Date	2011-10-25 12:37 +0200
Organization	MagistratWien newsserver
Message-Id	<1319539080.265361@proxy.dienste.wien.at>

Show all headers | View raw

I wrote:
>> If you've never made any changes to the tables/indexes, why
>> would VACUUM touch those files?  (i.e., assuming the DB had been
>> vacuumed prior to being cast in stone)
>
> I don't know the server code well enough to answer that question
> without some research.

[...]

> To really get definite answers which files in the data directory
> will never change, you should look for somebody who knows
> PostgreSQL better than I do. I suggest asking the pgsql-hackers
> mailing list.

I decided to increase my knowledge by playing around a little,
and it turns out that you need write permission even to *read*
a table. The file is opened with "O_RDWR | PG_BINARY", so even
SELECTing from a table whose file is read-only will give you
ERROR:  could not open file "base/17046/17047": Permission denied

That's no bug, because a SELECT can cause writes (update the
hint bits).

So in order to have something like PostgreSQL tables on read-only
media, you'd definitely have to hack up PostgreSQL.

Yours,
Laurenz Albe

Back to comp.databases.postgresql | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Constraints for R/O ./data/{base, et al.} Don Y <nowhere@here.com> - 2011-09-28 08:58 -0700
  Re: Constraints for R/O ./data/{base, et al.} Mladen Gogala <gogala.mladen@gmail.com> - 2011-09-28 18:51 +0000
  Re: Constraints for R/O ./data/{base, et al.} "Laurenz Albe" <invite@spam.to.invalid> - 2011-09-29 09:37 +0200
    Re: Constraints for R/O ./data/{base, et al.} Don Y <nowhere@here.com> - 2011-10-06 22:17 -0700
      Re: Constraints for R/O ./data/{base, et al.} "Laurenz Albe" <invite@spam.to.invalid> - 2011-10-07 10:10 +0200
        Re: Constraints for R/O ./data/{base, et al.} Don Y <nowhere@here.com> - 2011-10-07 11:12 -0700
          Re: Constraints for R/O ./data/{base, et al.} Mladen Gogala <gogala.mladen@gmail.com> - 2011-10-08 05:48 +0000
          Re: Constraints for R/O ./data/{base, et al.} "Laurenz Albe" <invite@spam.to.invalid> - 2011-10-10 16:48 +0200
            Re: Constraints for R/O ./data/{base, et al.} "Laurenz Albe" <invite@spam.to.invalid> - 2011-10-25 12:37 +0200

csiph-web